The EU aims to boost online cross-border sales and stop "geo-blocking" - restricting offers based on a customer's location - which runs counter to its goal of a single market for digital goods and services that would underpin economic growth.

"E-commerce should give consumers a wider choice of goods and services, as well as the opportunity to make purchases across borders," European Competition Commissioner Margrethe Vestager said in a statement.

The European Commission investigations, launched after a nearly two-year inquiry, will look into whether the companies are breaking EU competition rules by unfairly restricting retail prices or by excluding customers from certain offers because of their nationality or location.

The Commission said in a statement that such curbs were widespread in the 28-country bloc.

The consumer electronics investigate targets Taiwan's Asus  (>> ASUSTEK Computer Inc.), Denon & Marantz, Philips (>> PHILIPS) and Pioneer (>> Pioneer Corp), suspected of having restricted the ability of online retailers to set their own prices for appliances, notebooks and hi-fi products.

For video games, Valve Corp, the owner of the Steam distribution platform and five game makers - Bandai Namco (>> Bandai Namco Holdings Inc), Capcom (>> CAPCOM CO., LTD.), Focus Home (>> Focus Home Interactive), Koch Media and ZeniMax - accused of preventing purchases because of a consumer's location or country of residence.

The effect would be to prevent consumers from being able to benefit from lower prices available elsewhere.

The Commission said it had also responded to complaints about hotel accommodation, specifically that room availability and prices varied according to where the customer is located.

This investigation concerns agreements between tour operators Kuoni, REWE [REGRP.UL], Thomas Cook (>> Thomas Cook Group plc) and TUI and hotel group Melia (>> Melia Hotels International SA).

Thomas Cook said it noted the Commission's decision to investigate and that it would cooperate fully.

"Across our 15 European source markets, Thomas Cook is committed to fair and open competition," it said in a statement.

Melia Hotels said the investigation did not imply any infringement had taken place and that the Commission was simply gathering information.

"Meliá will continue to collaborate with the Commission both actively and constructively ... trusting in a speedy solution to the procedure that will confirm the absence of any undue conduct concerning the rights of European consumer," the Spanish hotel chain said.

Companies face fines up to 10 percent of their global turnover if found guilty of breaching EU rules.

The Commission stressed the opening of formal proceedings did not prejudge the outcome and that there was no legal deadline to bringing an antitrust investigation to a close.

The Commission has proposed a ban on online retailers stopping a customer in one EU country from buying from a website in another, although this would not initially apply to copyright-protected items such as e-books, music and games.

It has also sought to increase transparency of prices for cross-border parcel delivery.

(Additional reporting by Robert Hetz; Editing by Philip Blenkinsop and Tom Heneghan)

By Foo Yun Chee